Muscle memory is good, but also how complacent accidents can happen. Especially if we are talking about loading and unloading. You want visual confirmation every time, and if possible, physically with a finger (your brain can be blind to things it does not expect to see.)
One can do dry fire drills and practice to get more familiar with ones firearm while at home and not expending ammo. These run through steps needed for use, with out any live ammo. One can use snap caps, but those can be a bit flaky on how well they work (meaning they may jam vs feed). Do keep any and all ammo out of the room if one does dry fire drills. It is a good way to practice sight picture, grip, manipulation of controls, and draw if a handgun.
Absolutely adrenaline and pressure can lead to one making operational errors. It won’t help you in every scenario where you don’t have any time to prepare. But like any unfamiliar task, from driving to operating dangerous machinery like saws, be mindful. Personally I find visualization helps in down times. When I first started to learn to drive, I was pretty shitty. I would visualize while in bed driving, going over all the stuff I was supposed to be remembering, and my learning curve quickly flattened out.
Action shooting sports is a fun and safe way to learn how to work a fire arm under stress and one can gauge their score on how well they are progressing. Of course, I am not doing any of those in the Now Now, and don’t encourage anyone to do so until the After-Times.
But I completely agree that familiarity and practice and training is needed to optimize a firearm for self defense. Hence my original post saying now is not the best time to be a first time gun owner. 
But if they are painting blue dots outside your house, I understand the reason to become one.
